1. Field of the Invention
The present invention relates to an optical fiber preform manufacturing apparatus and an optical fiber preform manufacturing method.
2. Description of the Related Art
As methods of manufacturing an optical fiber preform, the VAD method or the outside vapor phase deposition method is known.
FIG. 7 is a vertical cross-sectional view showing the schematic configuration of a conventional optical fiber preform manufacturing apparatus using the VAD method.
As shown in FIG. 7, an optical fiber preform manufacturing apparatus 101 includes a reaction chamber 110, a target member 120, a core burner 130, and a cladding burner 140.
The target member 120 is provided within the reaction chamber 110.
The core burner 130 and the cladding burner 140 deposit glass particles at the tip (lower part) of the target member 120 in the axial direction.
In addition, the related-art optical fiber preform manufacturing apparatus using the outside vapor phase deposition method is not provided with the core burner 130, and includes only the cladding burner 140.
The target member 120 is a rod-shaped member formed from, for example, quartz, extends in the vertical direction, and is provided within the reaction chamber 110.
The target member 120 is supported by a column 122 via a holding portion 121.
The column 122 is provided with a drive device (not shown in the drawings) that rotates the target member 120 around the central axis thereof and moves the target member in the direction of the central axis.
The core burner 130 is a burner that deposits glass particles used in order to form a core at the tip (lower part) of the target member 120 in the axial direction, and produces core soot S1.
The cladding burner 140 is a burner that deposits glass particles used in order to form cladding at an outer periphery of the core soot S1, and produces cladding soot S2.
By producing the core soot S1 and the cladding soot S2 in the axial direction at the tip (lower part) of the target member 120, an optical fiber porous preform S (hereinafter simply referred to as a porous preform S) is manufactured.
An optical fiber preform is fabricated by subjecting the manufactured porous preform S to dehydration processing and transparent vitrification by heating.
Moreover, after deficient cladding is adjusted if needed, an optical fiber is manufactured by drawing an optical fiber preform.
It is required that as few air bubbles as possible are present inside an optical fiber preform to be manufactured.
This is required in order to prevent a situation in which air bubbles reduce the strength of the optical fiber after drawing and increases the transmission loss of light.
As a cause of the generation of air bubbles within the optical fiber preform, for example, the mixing of dust into the porous preform S during manufacture is an exemplary example.
In order to suppress generation of air bubbles, a reaction chamber is disposed inside a booth, and clean air is introduced into the booth, thereby reducing dust within the reaction chamber (for example, refer to Japanese Unexamined Patent Application, First Publication No. H7-300332).
That is, as shown in FIG. 7, the optical fiber preform manufacturing apparatus 101 is provided with a booth 150 in which a reaction chamber 110 is disposed, an air supply device 160 for supplying clean air into the booth 150, and an exhaust device 180 that discharges air in the reaction chamber 110 to the outside.
In addition, the exhaust device 180 is coupled to a reaction chamber exhaust port 111 formed in the reaction chamber 110.
By operating the air supply device 160, clean air is supplied into the booth 150.
A side wall of the reaction chamber 110 is provided with an opening having a greater diameter than the diameter of the cladding burner 140, and the cladding burner 140 is fitted into the opening.
The clean air supplied into the booth 150 from a gap between the opening and the cladding burner 140 flows into the reaction chamber 110.
Since air within the reaction chamber 110 is discharged to the outside by the operation of the exhaust device 180, the clean air supplied into the booth 150 is discharged to the outside through the inside of the reaction chamber 110.
Accordingly, the optical fiber preform manufacturing apparatus 101 including the booth 150, the air supply device 160, and the exhaust device 180 can reduce the amount of dust in the reaction chamber 110.
Hence, a certain advantage that the amount of dust mixed into the porous preform S can be reduced, and air bubbles in an optical fiber preform can be suppressed is obtained.
However, since a worker enters the booth 150 and works during the maintenance of the optical fiber preform manufacturing apparatus 10, dust is generated within the booth 150.
Additionally, the glass particles that have not been deposited on the target member 120 adhere to the inside of the reaction chamber 110, or soot cracking of the porous preform S during manufacture occurs, whereby soot powder is generated.
For this reason, it is necessary to clean the reaction chamber 110 or the booth 150.
The cleaning work is also performed within the booth 150 by a worker.
Dust, such as soot powder generated during maintenance or cleaning, adheres to the inside (particularly, a floor surface 151) of the booth 150.
When manufacture of the porous preform S is again started after maintenance or cleaning, there is a possibility that the flow of air will be generated within the booth 150 by the operation of the air supply device 160, and the dust adhering to the inside of the booth 150 will be lifted.
Additionally, since the exhaust device 180 discharges air within the reaction chamber 110 via the reaction chamber exhaust port 111, the flow of air that goes into the reaction chamber 110 is generated from the inside of the booth 150.
As the lifted dust flows along such air flow, this dust enters the reaction chamber 110, and is mixed into the porous preform S during manufacture.
That is, there is a problem in that the number of air bubbles within a manufactured optical fiber preform increases after maintenance or cleaning.
Additionally, since an increase in air bubbles within the optical fiber preform is seen, manufacture cannot be resumed during a certain period of time after maintenance or cleaning is performed.
Therefore, there is a problem in that the processing capacity of the optical fiber preform manufacturing apparatus 101 declines.